I shall investigate the regulation by light of the levels of mRNAs coding for two specific polypeptides. These two polypeptides are the small subunits of ribulose 1,5 bisphosphate carboxylase, which is the major soluble chloroplast protein, and the chlorophyll a/b-binding protein, which is the major protein of chloroplast membranes. I propose to develop a cloned plasmid sequence corresponding to the ribulose 1,5 bisphosphate carboxylase small subunit mRNA to use as a probe to quantitatively detect the presence of this coding sequence in the plants under various light conditions. In addition I shall continue using in vitro translation of mRNA coupled with immunoprecipitation of specific translation products as an assay for translatable mRNA coding for specific polypeptides. The combination of these methods will allow me to examine the possible regulation by light or transcription, processing and/or translation of these specific mRNAs. I shall also determine the action spectrum for the light response in order to identify the photoreceptor for the response.